To evaluate the value of second trimester serological screening of Down syndrome (DS) in pregnant women with advanced age.

From January 2009 to December 2014, a total of 1 571 cases of pregnant women with advanced age (expected age of delivery≥35 years old) who received second trimester serological screening for DS in Department of Prenatal Diagnosis of Obstetrics and Gynecology, West China Second University Hospital were enrolled as advanced age group (n=1 571). From January to December 2012, a total of 10 881 cases of young pregnant women (expected age of delivery<35 years old) who received second trimester serological screening of DS in the same hospital were chose as young group (n=10 881). The inclusion criteria for subjects in this research were as follows: pregnant women, gestational age of 14 to 20^{+ 6} weeks, singleton pregnancy, voluntary to do second trimester DS serological screening. The exclusion criteria for subjects: bearing a family history of congenital malformations or chromosomal abnormalities, associated with other internal or surgical diseases, bigeminal or multiple pregnancy and patients with diabetes. Three second trimester maternal serum screening markers, free β-human chorionic gonadotrophin (β-hCG), alpha fetoprotein (AFP) and unconjugated estriol (uE₃) were used for DS serological screening. Patients with an increased risk of DS (≥l/270) were offered genetic amniocentesis to ensure whether the fetus was DS or not, and the pregnancy outcomes of other pregnant women who didn't received genetic amniocentesis were obtained by telephone follow-up. The false positive rate and screening efficiency of DS serological screening were evaluated in both two groups and were compared by statistical methods. The study protocol was approved by the Ethical Review Board of Investigation in West China Second University Hospital. Informed consent was obtained from each patient before receiving second trimester DS screening. There were no statistical differences of gestational age and weight between groups (P>0.05).

①Among 1 571 cases of pregnant women in advanced age group, 121 cases were in high-risk of DS serological screening, and 4 cases were diagnosed as DS; 1 450 cases were in low-risk of DS serological screening, and no fetal DS was found. Among 10 881 cases of pregnant women in young group, 759 cases were in high-risk of DS serological screening, and 6 cases were diagnosed as DS; 10 122 cases were in low-risk of DS serological screening, and 1 case were diagnosed as DS postnatally. ②In advanced age group, the false positive rate of DS serological screening was 7.4% (117/1 571), the young group was 6.9% (753/10 881), and the difference was not statistically significant (χ²=0.587, P=0.444). ③In advanced age group, DS serological screening efficiency was 3.3% (4/121), which was significantly higher than that of young group (0.8%, 6/759), and the difference was statistically significant (χ²=3.870, P=0.049).

The three-marker (β-hCG, AFP and uE₃) test is an effective screen strategy for second trimester serological screening of DS in pregnant women with advanced age. It can reduce the rate of genetic amniocentesis.